Add allow_nil qualifier to validate_presence_of

[cjmao]

Rails supports validates :some_attribute, presence: { allow_nil: true } on models, but currently the validate_presence_of matcher doesn't have the allow_nil qualifier.

It will be much simpler to write specs with this added.
Please let me know if it is not added for some reasons.

[mcmire]

Hey @cjmao,

There is an existing issue for this in #683. We have not seen much of a need for this -- after all, usually when you are using validates_presence_of you want to prevent an attribute from being nil or an empty string. So that's why it hasn't been added, but if there is a legitimate use case, then we would gladly take a PR. There was a PR that someone started in #695 which you may use as inspiration if you wish; you may want to read the comments for that particular use case however before starting.

[cjmao]

Thanks @mcmire , I've read the comments under the issue and the PR you mentioned. Seems this is a duplicate issue, and my use case is mostly the same with those in the comments.

Currently i'm having a model which has a description attribute. A user can optionally choose to write some description in the description field of a form, or leave the field blank. When the form is posted, and the user choose not to write any description, the controller will receive an empty string as the parameter for description.

Since this field is optional, I think it's best to convert (only) empty string to nil (a user cannot type an empty string, so it's reasonable to consider empty strings to be nil to indicate that the user typed nothing).
With this, the app can distinguish between whether the user has typed nothing, or has typed something which is considered blank. If the user did type something blank (not empty), the app should warn that the user should provide something meaningful (not blank).

So in this case, it indeed needs to validate the presence of this attribute, but only when it is not nil, which comes to validates :description, presence: { allow_nil: true }.

[mcmire]

@cjmao Okay, thanks for that. Well, like I said, if you want to start a new PR based on the one that exists that would be great, and we can slip it into the next release.

[cjmao]

@mcmire thanks for the advice!
I don't have much experience with Ruby though, I'll see what i can do. 😂

[mcmire]

Just looking over old issues. I'm going to close this since we have a PR for this.